fvp-linux.rootfs+rst31: Extend timeout to 21min

Case:
https://ci.trustedfirmware.org/job/tf-a-builder/1657283/console
https://tf.validation.linaro.org/scheduler/job/1311439

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I97f625d37ed9bc804041d9b41c0f405ddcea52ed
(cherry picked from commit 9dd496245c89efed6dd573340de358fbd4977149)
diff --git a/run_config/fvp-linux.rootfs+rst31 b/run_config/fvp-linux.rootfs+rst31
index bd58213..06c703b 100644
--- a/run_config/fvp-linux.rootfs+rst31
+++ b/run_config/fvp-linux.rootfs+rst31
@@ -12,7 +12,7 @@
 }
 
 generate_lava_job_template() {
-	uart="0" timeout="1800" lava_timeout="1140" file="linux-oe-rst-bl31.exp" track_expect
+	uart="0" timeout="1800" lava_timeout="1260" file="linux-oe-rst-bl31.exp" track_expect
 
 	payload_type="linux" gen_fvp_yaml_template
 }